The donor states that it was used from the 1920s through to the 1940s; identical item on website dated to 1930s.
Measurement numbers from 1 to 180 degrees going both ways on the circular edge; "No 19 // THE L.S. STARRETT CO. // ATHOL. MASS. U.S.A." engraved on the protractor; "READ INSIDE SCALE // READ OUTSIDE SCALE" written in pen on a piece of tape on the handle